1. Field of the Invention
This invention relates to lithium-alloy/molten salt/metal sulfide batteries. More particularly, the present invention relates to a new and novel cell design of lithium-alloy/molten salt/metal sulfide batteries without the use of costly materials utilizing simple fabrication techniques.
2. Description of the Prior Art
Lithium-alloy/metal sulfide batteries have positive and negative electrodes which are electrically insulated from one another by separators. Typically, the negative electrode material is lithium-alloy (generally LiAl), the positive electrode material is an iron sulfide (FeS or FeS.sub.2) and the separators are formed of a fibrous boron nitride (BN) or a pressed powder magnesium oxide (MgO). An electrolyte such as a lithium chloride and potassium chloride mixture(LiCl-KCl)is normally infiltrated into the electrode materials and into the separators. The positive and negative current collectors are commonly formed of a conductive open mesh-like sheet or plate construction so as to confine the electrode materials while also allowing the migration of the electrolyte as required relative to the confined electrode materials. Full size batteries of this type are comprised of many cells, each having the construction noted above, that are housed together in a common battery housing and that are electrically connected in series to produce higher effective voltage output.
This type of battery or cell is designed to operate at temperatures in the range of 350.degree.-500.degree. C. The electrode materials and electrolyte are most corrosive in these temperatures. Accordingly, the current collectors must be formed from a corrosion-resistant, yet electrically-conductive, material. Moreover, the battery is designed to have an operating life in excess of 1000 "deep discharge" cycles, where each "deep discharge" cycle means discharging the fully charged battery down to approximately only a 20% charge level before recharging it again. During this deep discharge cycling, the positive and negative electrode materials undergo volumetric changes at different rates. This can shift the physically confining respective current collectors relative to one another within the battery cell or can even deform the collectors and/or cell housing. Also, nonuse of this type battery allows the operating temperatures of the electrolyte and electrode materials (each a paste-like liquid at the operating temperatures) to drop to temperatures at which they can freeze solid. These freeze-thaw cycles can also cause movement between the current collectors, electrode materials and cell housing.
U.S. Pat. No. 4,540,642 describes a lithium-alloy/iron sulfide cell wherein the lithium-alloy/iron sulfide cell having an open-ended cell housing having positive and negative electrode subassemblies that are nested within one another (the positive subassembly being located outwardly of the negative subassembly) and separator structure sandwiched between the subassemblies electrically insulating them from one another, and the subassemblies being fitted into the cell housing and defining cavities open respectively to the opposite open ends of the cell housing.
U.S. Pat. No. 4,357,398 illustrates the design of a secondary, high temperature electrochemical cell for use in lithium-alloy negative electrodes, transition metal chalcogenide positive electrodes and alkaline metal halide or alkaline earth-metal halide electrolyte.
U.S. Pat. No. 4,306,004 discloses an electrode structure for a secondary electrochemical cell in which the electrodes are separated by ceramic materials.
The cell designs as exemplified in the above patents, all require the use of costly materials as well as complex fabrication techniques which result in a high cost cell. The high costs of these cells prohibit their use in many commercial and consumer applications.